1. Field of the Invention
The present invention relates to a semiconductor device and a semiconductor display device correcting system. Particularly, the present invention relates to a semiconductor display device in which a pixel, a driving circuit, and a peripheral circuit such as a nonvolatile memory are integrally formed on an insulating substrate by using an SOI (Silicon On Insulator) technique. Moreover, the present invention relates to a correcting method of a semiconductor display device. Silicon set forth in the present specification indicates single crystal or substantially single crystal.
2. Description of the Related Art
In recent years, a technique for manufacturing a semiconductor device, such as a thin film transistor (TFT), in which a semiconductor thin film is formed on an inexpensive glass substrate has been rapidly developed. The reason is that the demand for an active matrix type liquid crystal display device (liquid crystal panel) has increased.
The active matrix type liquid crystal panel is constructed such that a TFT is disposed for each of several tens to several millions of pixel regions arranged in matrix, and an electric charge going in and out of each pixel electrode is controlled by the switching function of the TFT.
FIG. 23 shows a conventional active matrix type liquid crystal display device. As shown in FIG. 23, the conventional active matrix type liquid crystal display device includes a source line side driver 2301, a gate line side driver 2302, a plurality of pixel TFTs 2303 arranged in matrix, and a picture signal line 2304.
The source line side driver and the gate line side driver include a shift register, a buffer circuit, and the like, and are integrally formed on the same substrate as an active matrix circuit in recent years.
Thin film transistors using amorphous silicon formed on a glass substrate are disposed in the active matrix circuit.
There is also known a structure in which quartz is used for a substrate and a thin film transistor is formed of a polycrystalline silicon film. In this case, both a peripheral driving circuit and an active matrix circuit are constituted by thin film transistors formed on the quartz substrate.
There is also known a technique in which a thin film transistor using a crystalline silicon film is formed on a glass substrate by using a technique such as laser annealing. When this technique is used, an active matrix circuit and a peripheral driving circuit can be integrated on a glass substrate.
In the structure as shown in FIG. 23, a picture signal supplied to the picture signal line 2304 is selected by a signal from a shift register circuit of the source line side driver (shift register for horizontal scanning). Then the designated picture signal is supplied to the corresponding source signal line.
The picture signal supplied to the source signal line is selected by a thin film transistor of a pixel and is written into the designated pixel electrode.
The thin film transistor of the pixel is operated by a selection signal supplied from a shift register of the gate line side driver (shift register for vertical scanning) through a gate signal line.
This operation is sequentially repeated at suitable timing by signals from the shift register of the source line side driver and signals from the shift register of the gate line side driver, so that information is sequentially written into the respective pixels arranged in matrix.
In recent years, an active matrix type liquid crystal display device has been often used for a note-sized personal computer. In the personal computer, a liquid crystal display device is required to realize such functions that a plurality of application programs are concurrently started up or a picture from a digital camera is taken in and is processed, that is, a liquid crystal display device capable of realizing large screen, high resolution, and multi-gradation display is required.
Moreover, the demand for a liquid crystal projector which can project a television signal such as a high-definition television signal and can realize a large screen, has increased. In this case as well, the quality of a provided picture depends on the degree of fineness of gradation display.
As described above, for the purpose of providing a high quality picture, it is important to what degree the gradation display can be made fine. As a system of gradation display, there are a system (analog gradation) of supplying an analog signal such as a video signal or a television signal to a source line and a system (digital gradation) of supplying a digital signal from a personal computer or the like to a picture signal line.
In the analog gradation, as described above, analog picture signals to be supplied to the picture signal line are sequentially selected by signals from the source driver, and the designated picture signal is supplied to the corresponding source line.
In the digital gradation, digital signals to be supplied to the picture signal line are sequentially selected, and after D/A conversion, the designated picture signal is supplied to the corresponding source line.
In the case of the liquid crystal display device, even when any gradation display of the digital gradation and the analog gradation is used, the gradation display is realized by controlling the strength of transmitted light transmitting through the respective pixels of the liquid crystal panel by a voltage applied to the pixel. There is a relation between the voltage (V) applied to the pixel of the liquid crystal panel and the strength of transmitted light transmitting through the pixel as indicated by a dotted line in FIG. 24. However, it should be noted that in this place, there is shown an example in which the liquid crystal display device is in a TN (twisted nematic) mode and uses a normally white mode in which the device becomes in a light state when a voltage is not applied.
As is understood from FIG. 23 as well, there is a nonlinear relation between the voltage applied to the pixel of the liquid crystal panel and the strength of the transmitted light transmitting through the pixel. In other words, there is no linear relation between the voltage applied to the pixel and the strength of the transmitted light, so that it is difficult to control the strength of the transmitted light according to the applied voltage. Thus, it is difficult to realize desired gradation display.
In order to correct the above defect of the liquid crystal panel, a means called gamma correction is adopted. In the gamma correction, a voltage is corrected with respect to a supplied picture signal so that the strength of transmitted light is linearly changed according to an applied voltage. According to this gamma correction, excellent gradation display can be obtained. The relation between the applied voltage and the strength of the transmitted light in the case where the gamma correction is carried out is indicated by a solid line in FIG. 24. As shown by the solid line in FIG. 24, when the gamma correction is applied to the picture signal, the relation between the applied voltage and the strength of the transmitted light becomes almost linear, so that it becomes possible to control the strength of the transmitted light according to the applied voltage, and excellent gradation display can be made.
However, conventionally, in order to apply the gamma correction to a picture signal, an IC circuit is additionally required, that is, a substrate having an IC circuit must be additionally provided on the outside of the liquid crystal panel. Thus, although excellent gradation display can be realized, increase of the number of parts is caused and it is actually impossible to miniaturize a product.
Moreover, in the active matrix type liquid crystal display device, from the nature of the device, its display characteristics become slightly different from every liquid crystal panel produced. However, conventionally, the same IC chip used for gamma correction and the same data stored in the IC chip have been used for all liquid crystal panels. Thus, the display characteristics of each liquid crystal panel are not taken into consideration, so that complete gamma correction can not be made. Thus, the shipped liquid crystal panel products have variation in the precision of gradation display, which becomes a problem.
The present invention has been made in view of the above, and an object of the present invention is to provide a semiconductor display device, particularly to provide a liquid crystal display device, which is able to realize excellent gradation display without increasing the number of parts and is able to be miniaturized. Another object of the present invention is to provide a system for gamma correction of this semiconductor display device.
According to an aspect of the present invention, a semiconductor display device correcting system comprises means for supplying a digital picture signal; a semiconductor display device including a control circuit for carrying out gamma correction of the digital picture signal, and a memory for storing data used in the gamma correction; means for converting a picture displayed on the semiconductor display device into a digital signal; and means for comparing the digital picture signal with the converted digital signal, wherein the control circuit and the memory are constituted by TFTs, and are integrally formed on the same insulating substrate. The above object can be achieved by this structure.
The memory may be a nonvolatile memory.
The nonvolatile memory may include a plurality of FAMOS type TFTs.
The system may further comprise a volatile memory, and the volatile memory may be constituted by TFTs and may be integrally formed on the same insulating substrate as the control circuit and the nonvolatile memory.
According to another aspect of the present invention, a semiconductor display device correcting system comprises means for supplying a digital picture signal; means for converting the digital picture signal into an analog picture signal; a semiconductor display device including a control circuit for carrying out gamma correction of the analog picture signal, and a memory for storing data used in the gamma correction; means for converting a picture displayed on the semiconductor display device into a digital signal; and means for comparing the digital picture signal with the converted digital signal, wherein the control circuit and the memory are constituted by TFTs, and are integrally formed on the same insulating substrate. The above object can be achieved by this structure.
The memory may be a nonvolatile memory.
The nonvolatile memory may include a plurality of FAMOS type TFTs.
The system may further comprise a volatile memory, and the volatile memory may be constituted by TFTs and may be integrally formed on the same insulating substrate as the control circuit and the nonvolatile memory.
According to still another aspect of the present invention, a correcting method of a semiconductor display device comprises the steps of carrying out gamma correction of an inputted digital picture signal, converting the digital picture signal subjected to the gamma correction into a picture, converting the picture into a digital signal, obtaining gamma correction data by comparing the digital picture signal with the converted digital signal to obtain a difference therebetween and by returning the difference to the step of the gamma correction, and storing the gamma correction data in a memory. The above object is achieved by this method.
According to yet another aspect of the present invention, a correcting method of a semiconductor display device comprises the steps of converting a digital picture signal into an analog picture signal, carrying out gamma correction of the inputted analog picture signal, converting the analog picture signal subjected to the gamma correction into a picture, converting the picture into a digital signal, obtaining gamma correction data by comparing the digital picture signal with the converted digital signal to obtain a difference therebetween and by returning the difference to the step of the gamma correction, and storing the gamma correction data in a memory. The above object is achieved by this method.